DNA Structure and replication

Question 1

Characteristic properties of DNA as hereditary material

Answer 1

1. high capacity for information storage + chemically stable to encode information without fail, can’t change easily due to agem nutrition or environment
2. replicate accurately
3. be capable of variation

Question 2

Structure of DNA

Answer 2

• nucleic acids exist as polymers called polynucleotides
• each nucleotide is composed of monomers called nucleotides

Question 3

structure of nucleotide?

Answer 3

1. 5 carbon sugar, ie pentose
2. nitrogenous base
3. phosphate group

5 carbon sugar + nitrogenous base = nucleoside
all 3 = nucleotide

Question 4

what are the two types of nucleic acids

Answer 4

Deoxyribonucleic acid (DNA):
- pentose sugar is deoxyribose
- deoxyribonucleotides are monomers of RNA

Ribonucleic acid (RNA)
- pentose sugar is ribose
ribonucleotides are monomers of RNA

Question 5

pentose sugar structure

Answer 5

• 5-carbon sugars, occur as ring forms
• In nucleic acids, the 5’ carbon is linked in an ester bond to the phosphate group and the 1’ carbon is linked in a glycosidic bond to the nitrogenous base.
• Two types of pentose (ribose and deoxyribose), they distinguish DNA from RNA.

Main difference between the ribose and deoxyribose sugars:
- deoxyribose: At the 2’ carbon, the hydroxyl group (-OH) is replaced by a hydrogen atom (H).
- leads to significant differences in structure and
functions of the two types of nucleic acids.
- in RNA: partial negative charge of the hydroxyl group in ribose repels the negative charge of the phosphate -> preventing the RNA chain from coiling in as tight a helix as it does in DNA -> RNA more susceptible to chemical and enzyme degradation

Question 6

nitrogenous bases

Answer 6

• has nitrogen-containing ring structure
• two types: purines and pyrimidines
• purines: 6-membered ring fused to a 5-membered ring (Adenine and Guanine)
• pyrimidines: 6-membered ring (Cytosine and Thymine/Uracil)

Question 7

what is a nucleoside

Answer 7

• combination of a pentose with a nitrogenous base
• condensation rxn as it occurs with elimination of water
• 1’ carbon of pentose is linked in glycosidic bond to nitrogenous base
  (ref to page 7 for diagram)
• two types: ribonucleosides and deoxyribonucleosides

Question 8

what is a nucleotide + how does number of phosphate groups vary

Answer 8

nucleotide: formed by further condensation between nucleoside and phosphate group, forming a phosphoester bond between 5’ carbon of pentose and phosphate group

number of phosphate groups varies from 1-3
- 1 phosphate group → nucleoside monophosphate (e.g. AMP, adenosine monophosphate)
- 2 phosphate groups → nucleoside diphosphate (e.g. ADP, adenosine diphosphate)
* 3 phosphate groups → nucleoside triphosphate (ATP, adenosine triphosphate)

Question 9

formation of di and polynucleotides

Answer 9

• dinucleotide: condensation between 5’-phosphate group of one nucleotide and 3’-hydroxyl group of the other to form phosphodiester bond
• phosphodiester bonds between 5’ phosphate and 3’ hydroxyl groups of nucleotides form linear, unbranched sugar-phosphate backbone
• phosphodiester bonds are strong covalent bonds, confering strength and stability on the polynucleotide chain, preventing breakage of the chain during dna replication

Question 10

polarity / directionality in polynucleotide

Answer 10

manner in which deoxyribonucleoside triphosphates are added to the 3’ end of a growing chain has resulted in a polynucleotide molecule that has polarity or directionality

each DNA / RNA strand has two free ends that are chemically different from each other
- 5’ end with free 5’ carbon carrying phosphate group
- 3’ end with free 3’ carbon carrying a hydroxyl group

dna / rna base sequence read in 5’ to 3’ direction